If you are talking about having different textures on the insde and the outside of a wall. Open one of the .FPS files out of the ww2 segments section in Note Pad or FPI edit pad.
Notice that there are 16 objects that make up a standard vanilla segment. Usually the last eight are the exterior of the wall and the ceiling.
Modify the textures listed and save the file as a different name. Paint the interior walls as stated above. You will see the floor pattern rotate as you place these walls. You should play and practice doing this before you try it in your working game map.
Hope this helps
Nothing but coffee in my veins 'Insomnia is Coming'
